Breeding improved tomato varieties involves providing genetics that give an advantage to the grower, processor, consumer, or other member of the supply chain. The improvement may be in the form of field performance, disease resistance, factory performance, or a fruit quality characteristic. For a tomato variety to be suitable to be grown for processing, the variety must have a concentrated fruit setting and maturity, firm fruit, and sufficient rot tolerance to allow early fruit to remain rot-free while later fruit continues to develop and ripen.
Most commercial processing tomato varieties are hybrids resulting from a cross pollination of two true-breeding, inbred parents. Through the use of true-breeding lines, a hybrid is produced that often displays characteristics of each parent, and often demonstrates characteristics that are superior to either parent alone, or that allow a hybrid to mask inadequacies of the individual parents.
Processing tomato varieties combining resistance to Verticillium wilt race 1 (Verticillium dahliae), Fusarium wilt race 1 and 2 (Fusarium oxysporum pv lycopersici), and root knot nematode (Meloidogyne incognita) are highly desirable in most climates around the world.
Moreover, in regions such as California, the industry has seen a considerable increase in pressure from tomato spotted wilt virus (TSWV). Thus, varieties with resistance to TSWV are in high demand by both growers and processors to ensure a productive crop cycle, particularly those with high field yield.
However, to be commercially viable, the tomato variety must perform acceptably in the field and factory as required by any other processing tomato variety.
Processing tomato quality parameters differ from those of fruit used in the fresh market. The processing characteristics are typically determined using a sample of hot-break tomato pulp or juice produced in a consistent manner to those familiar with the art. For example, a fixed mass of tomatoes may be cooked in a microwave oven for several minutes to halt any enzymatic breakdown of the sample, lost water is replaced, and the sample is pulped to remove skins and seed to produce a uniform juice sample. The juice sample can be analyzed for various quality parameters important to processing tomato including but not limited to gross viscosity measures such as juice Bostwick, soluble solids measures using a refractometer (°Brix), measures of acidity and pH, and measures of color for example a Hunter a/b score. The value of these traits depends on the product that is being commercially produced by the processing factory. In some instances, a factory will put a higher value on a thick viscosity variety, whereas in other instances, a thin viscosity will make a superior product.